A common method of forming structures on wafers or other substrates in the semiconductor industry is lithography. In lithography, features are formed by the addition or removal of material on a substrate surface. In general, lithography proceeds by coating a surface with a resist. Light is projected onto the resist through a mask, exposing portions of the resist to the projected light and patterning the resist. Depending on the resist, the light causes alterations in the chemical structures of the resist, which upon the application of a developer either allows the exposed portions of the resist to be removed or prevents the exposed portions of the resist from being removed. Once a portion of the resist is removed, the exposed substrate surfaces may be etched.
Perceived limitations in photolithography, including the optical diffraction limit, spurred the development next-generation lithography techniques, including extreme ultraviolet lithography (EUV), which utilizes electromagnetic radiation having wavelengths in the range of 10 nm to 124 nm, including all values and ranges therein. In one form of extreme ultraviolet lithography, plasma is formed from xenon. In generating the plasma, electrons are liberated, and the plasma radiates light at wavelengths of approximately 13 to 14 nanometers. The light interacts with various optics, such as one or more condensers, lenses, and mirrors, and is projected onto a mask (which may be formed on a mirror) and reflected onto a resist coated workpiece, such as a wafer. The process is performed under relatively high vacuum conditions as all matter absorbs extreme ultraviolet light radiation.
The resist is commonly formed from compositions that include organic compounds. For example, resist formulations may include a resin, a solvent, a photoacid generator and a quencher. Any of the formulation components may include organic compounds. Even in resists that are inorganic or include inorganic compounds, such as hafnium oxide sulfate (HfSOx) or photosensitive metal organic oxides, organic compounds may be present. During processing, the organic compounds, or derivatives thereof, may be fragmented and thus liberated due to outgassing (or off gassing) and other effects. The organic compounds may then be deposited onto the lens, mask, and other surfaces of the extreme ultraviolet optics and masks. This residue build up may cause defects in the optics and mask that may negatively affect the performance of the process.
However, there are many difficulties in obtaining relatively effective cleaning solutions for extreme ultraviolet lithography components including lack of infrastructure and inspection ability and the need for further tool and process development. Furthermore, extreme ultraviolet surface materials, such as absorber, anti-reflective coatings and capping layers on the masks are not fully established, making it difficult to target specific cleaning chemistries. In addition, there are few suppliers and the market is relatively small leading to a general lack of market force behind the development of solutions.